Hydrostatically driven machines are well known in the art. In some of these machines, a pair of hydrostatic units are used to individually provide power to the associated right or left drive units. Each of the hydrostatic units include an engine driven pump fluidity connected in a closed loop to a hydraulic motor which transmits torque therefrom. In order to steer the machine, the speed of one of the hydrostatic units is either increased or decreased with respect to the other hydrostatic unit. In other machines, a single hydrostatic unit is used to transmit power from the engine to the respective drive units through a differential. It has been known to use clutch/brake type steering but this does not provide constant power to both drive units during steering. It has also been known to provide a differential steer mechanism having a hydraulic steer motor operative to input a torque to the differential steer mechanism to change the relative speed outputs to each of the drive units to provide steering. In these known differential steer mechanisms, the hydraulic steer motor is connected to a dedicated pump or it receives fluid from an implement pump. These known arrangements either require an extra pump or an oversized implement pump.
The present invention is directed to overcoming one or more of the problems as set forth above.